<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>

<body>
  <div id="app"></div>

  <template id="why">
    <div>
      <h2>{{ message }}</h2>
      <h2>{{ counter }}</h2>
      <button @click="increment">+1</button>
      <button @click="decrement">-1</button>
      <button @click="btnClick">按钮</button>
    </div>
  </template>

  <script src="https://unpkg.com/vue@next"></script>
  <script>
    Vue.createApp({
      template: '#why',
      data: function () {
        return {
          message: "Hello World",
          counter: 100
        }
      },
      // 定义各种各样的方法
      methods: {
        increment() {
          this.counter++;
        },
        decrement() {
          this.counter--;
        },
        btnClick: () => {
          // this === window ? 不可以
          // 写成一个箭头函数时，这个this就是window
          // 在箭头函数中不绑定this
          console.log(this);
        }
      }
    }).mount("#app");


    // const foo = function () {
    //     console.log(this);
    // }
    const foo = () => {
      console.log(this);
    }
    foo(); // window

    const obj = {
      bar: foo
    }
    obj.bar(); // obj
  </script>
</body>

</html>